This invention relates to the processing of tobacco, particularly, but not necessarily, Burley tobacco.
Burley tobacco generally requires heat treatment to improve its flavour and aroma characteristics before it is used in tobacco products.
Known methods of treating Burley tobacco involve heating Burley lamina which has been cased to produce a toasted character on heating. Casings are predominantly mixtures of sugars, cocoa, licorice and humectants, the sugars of which, when heated to an appropriate temperature and for an appropriate time lead to the formation of components which give favourable aroma/sensory attributes. Two basic types of reactions result in the production of these favourable components (often referred to in the tobacco industry as xe2x80x9ctoastingxe2x80x9d); reactions of reducing sugars with components possessing a free amino group (Maillard reactions) and reactions in which sugars are heated in the absence of amino groups (browning reactions). Browning reactions generally require higher temperatures than Maillard reactions. The formation of favourable aroma compounds depends on the product temperature, residence time and tobacco input/output moisture.
The maximum temperature to which the Burley tobacco is subjected in known treatments, such as the Cased Leaf Drying process (such as the Proctor Cased Tobacco Dryer described in, Proctor and Schwartz, Inc. Dryer Handbook), is 1500xc2x0 C. and typically residence times of 190 seconds are used. However, because the temperature of the tobacco does not start to rise until all free unbound moisture is released (i.e. the critical moisture content is reached; see FIG. 2), the tobacco itself may not actually achieve this temperature during conventional treatments.
In order for the Burley tobacco to reach the temperature required for these chemical reactions to occur in the conventional treatments, the dryer output moisture content of the tobacco must be below 7%. At these low moisture levels, the tobacco is brittle and difficult to process without causing a detrimental effect on product quality. Therefore, after conventional heat treatment, the Burley tobacco must be cooled and re-wet to about 20% moisture so that it can be cut. After cutting, the Burley tobacco must then be dried again to moisture levels suitable for the manufacture of tobacco products (typically 12% to 16%).
U.S. Pat. No. 4,687,007 describes a process for the pressurised drying of a standard lamina tobacco blend incorporating flue-cured, oriental, Burley and reconstituted tobaccos in order to expand the blend and improve the quality, i.e. reduce the impact and irritation.
The present invention, in contrast, provides a process for heat treating Burley tobacco in a Burley processing line at elevated pressures which results in high tobacco temperature being achieved at a higher moisture content. The higher tobacco temperature improves the formation of aromatic and flavouring components at high tobacco moisture levels, so that the Burley tobacco can be produced at a moisture content suitable for cigarette production.
The present process allows the preparation of Burley tobacco for use in tobacco products to be simplified. Whereas in known processes, cased Burley tobacco has to be toasted, cooled, re-wet, cut and then dried to the final product moisture in separate stages, using the present process the Burley tobacco can be dried and toasted in one process stage to a desired product moisture. This line is known as a Burley processing line. As used herein the term xe2x80x9cBurley processing linexe2x80x9d means a line processing substantially only Burley tobacco, whether whole leaf, sliced or cut leaf, or stem or lamina parts only. The present invention results in a considerable saving in process time and cost.
It is also an object of the present invention to provide improved aroma of low quality processed Burley tobacco, and ideally subsequent taste and flavour of smoked cigarettes comprising Burley tobacco processed according to the invention.
It is also a further object of the present invention to provide processed Burley tobacco with improved aroma characteristics, without the need for addition of casing material.
The present invention provides a process of treating Burley tobacco in a Burley processing line, said process comprising heating Burley tobacco in a Burley processing line in a pressurised closed dryer to a tobacco temperature of 120xc2x0 C. or more at a pressure which is in the range of 0.25 to 7 Bar absolute, the moisture content of the Burley tobacco being maintained above 10% during the process, and the moisture content of the Burley tobacco exiting the system being greater than 10%, the aroma and/or taste and flavour characteristics of thus treated Burley tobacco being altered to become more toasted.
Preferably the process is performed in a pneumatically conveyed closed loop dryer.
Preferably pressurised superheated steam is the conveying and drying medium.
It is preferable that the Burley tobacco used in the process is pre-cut. Alternatively, the Burley tobacco may be cut after processing, as in conventional Burley treatment processes.
The Burley tobacco used in the pressurised process preferably has an input moisture content above 20%, preferably 25% or more, and even more preferably 30% or more, and may even be up to 45%, all by weight of the tobacco.
The input temperature of the tobacco in the pressurised process may be in the range of 20xc2x0 C. to 100xc2x0 C., and is advantageously above 50xc2x0 C.
Burley tobacco is fed into the dryer through a pressure tight feed inlet directly into a flow of superheated steam which is at a temperature of 200xc2x0 C. to 300xc2x0 C.
Preferably the superheated steam is at a temperature of 220xc2x0 C. or more, more preferably 230xc2x0 C. or more, depending on the pressure conditions and tobacco residence times utilised.
The tobacco is transported through the dryer suspended in the superheated steam.
The tobacco is heated by the steam to a product temperature of at least 120xc2x0 C., more preferably at least 130xc2x0 C. and most preferably at least 140xc2x0 C.
The dryer is preferably operated at pressures of from 1 to 7 Bar absolute, preferably above 2 Bar absolute and more preferably in the range of 3 to 7 Bar absolute.
The moisture loss from the tobacco may be from 5% to 30%, depending on the input moisture content of the tobacco and final moisture content required.
The residence time of the Burley tobacco at the elevated temperature and pressure may be from 5 to 25 seconds, more preferably 7 to 15 seconds. A short residence time may be 7-8 seconds and a long residence time may be 15 seconds. Residence time of the tobacco in the dryer will depend on the taste and flavour characteristics required.
The tobacco is then separated from the transport steam, for example in a high efficiency cyclone, and then discharged from the dryer through a pressure tight outlet.
After treatment, the moisture content of the tobacco, i.e. the exit moisture content, is advantageously from 10% to 25%, and is preferably 14% to 16%. The tobacco exit temperature from the dryer is in the range of 90xc2x0 C. to 1400C.
In addition to an improvement in sensory characteristics, the treatment may also result in some expansion of the Burley tobacco, so that the bulk density of the Burley tobacco is reduced after the process. Advantageously the tobacco is expanded by 5% or more, more advantageously by 10% or more and even more advantageously by 15% or more.
The raised pressure during the heat treatment allows the tobacco to be heated to higher temperatures than previous processes without drying out. The high temperature increases the rate of Maillard and browning reactions so the product has more aromatic reaction products than would otherwise be present. The drying treatment also releases ammonia from the tobacco. Once released, this becomes available to react with sugar groups in Maillard reactions. Ammonia is re-circulated around the dryer, if used, and is therefore more readily available for reaction to produce favourable aroma compounds. Because the higher temperatures required for the toasting reactions can be obtained without drying below normal final product moisture levels, i.e. about 7% in a Cased Leaf Dryer, the Burley product can be used in production without further wetting.
The Burley tobacco may advantageously undergo pre-treatment prior to pressurised drying, i.e. the process, in which pre-treatment it is heated at ambient pressure. This heating is optional and improves the penetration of the Burley tobacco during moistening or casing stages. The heating may be achieved by contacting the tobacco with steam. The temperature of the preheated tobacco is preferably in the range of 50xc2x0 C. to 100xc2x0 C. and may be in the range of 60xc2x0 C. to 70xc2x0 C.
Moistening may be achieved by introducing water into the tobacco to provide a tobacco moisture content of 45%, for example. The water is in the form of steam or steam atomised water droplets.
It may be desirable to in addition or in the alternative add casing to the Burley tobacco. Casings are flavourings designed to improve the flavour and aroma of tobacco. Casing solution may be introduced as part of the moistening water, preferably as droplets atomised in steam.
A cooling step may be carried out after the pressurised process to lower the temperature of the tobacco and thereby avoid cooling by evaporation of water. Cooling may be achieved by introducing tempered air into the tobacco stream. It is preferable that the product has a temperature of from 50xc2x0 C. to 60xc2x0 C. on exit from the cooling stage.
The present invention further provides a smoking material the product of the above process.
The present invention further provides a smoking article comprising a filter element attached to a smoking material rod wrapped in a wrapper, the rod comprising Burley tobacco material processed according to the invention.
The smoking article may comprise up to 100% of Burley tobacco processed according to the invention.
The present invention further provides a processed Burley smoking material exhibiting a more toasted character than processed Burley produced by a cased leaf dryer, the smoking material having one or more increased cocoa, caramellic, burnt sugar or nutty/roasted attribute (s) as described herein.
Preferably processed Burley smoking material has a significantly different caramellic attribute compared with a control material treated in a conventional cased leaf dryer (see Table 11).
The treatment process described above may also be used for other types of tobacco to reduce the bulk density thereof and confer favourable sensory characteristics.
The present invention further provides a process for treating tobacco stem or flue-cured lamina tobacco in a pressurised dryer comprising heating the stem or flue-cured lamina to a tobacco temperature up to 120xc2x0 C. at a pressure which is in the range of 0.25-4 Bar absolute, the moisture content of the tobacco being maintained above 10% during the process, and the moisture content of the tobacco exiting the dryer being greater than 10%, in order to provide a filling power improvement compared with conventional stem or flue-cured lamina processes.
The tobacco stem or flue-cured lamina is fed into the dryer through a feed inlet directly into a flow of superheated steam which is set at a temperature of 150xc2x0 to 300xc2x0 C.